CHIME-o-Grav: Wideband Timing of Four Millisecond Pulsars from the NANOGrav 15-yr dataset

TL;DR

This paper demonstrates the power of wideband timing by integrating CHIME’s high-cadence, low-frequency data with the NG15 dataset for four MSPs. Using a chimeric WB timing pipeline, it jointly estimates TOAs and DMs from each observation and refines binary, astrometric, and PK parameters through DMX, ELL1H, and enhanced noise modeling. Key results include a strong Shapiro-delay detection for PSR J2302$+$4442 with $m_c = 0.35^{+0.05}_{-0.04} M_{\odot}$ and $m_p = 1.8^{+0.3}_{-0.3} M_{\odot}$, plus improved $\dot{P}_{B}$ and $\dot{x}$ measurements for two other binaries, aided by VLBI-based distances and extended baselines. The work also illustrates solar-wind DM variability evident in CHIME data and discusses implications for PTA data volumes and solar-wind modeling in future analyses.

Abstract

Wideband timing of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) datasets, where a single time-of-arrival (TOA) and a single dispersion measure (DM) are measured using the entire bandwidth of each observation, was first done for the 12.5-year dataset, and proved to be invaluable for characterizing the time-varying dispersion measure, reducing the data volume, and for improving the overall timing precision. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) Telescope has been observing most NANOGrav millisecond pulsars (MSPs) at nearly daily cadence (compared to roughly monthly cadence for other NANOGrav observations) since 2019 with the objective of integration into future pulsar timing array (PTA) datasets. In this paper, we show the results of integration of high-cadence, low-observing-frequency CHIME data with data from the NANOGrav experiment for an isolated MSP PSR J0645$+$5158 and three binary MSPs PSR J1012$+$5307, PSR J2145$-$0750, and PSR J2302$+$4442. Using a wideband timing pipeline which we also describe, we present updated timing results for all four sources, including improvements in measurements of relativistic post-Keplerian parameters for the three binary pulsars in this analysis. For PSR J2302$+$4442, we report an updated strong detection of Shapiro delay from which we measured a companion mass of $0.35^{+0.05}_{-0.04}\ M_{\odot}$, a pulsar mass of $1.8^{+0.3}_{-0.3}\ M_{\odot}$, and an orbital inclination of ${80^{\circ}}^{+1}_{-2}$. We also report updated constraints on the reflex motion for PSR J2145$-$0750 using a combination of Very Long Baseline Array astrometry and our updated measurement of the time derivative of the projected semi-major axis of the pulsar orbit as a prior.

Figures (11)

• Figure 1: Top plot: timing resids for PSR J2145$-$0750; Middle plot: DM residuals; Bottom plot: DMX time series where vertical bars indicate DMX parameter uncertainty and horizontal bars indicate the width of DMX bins in time.
• Figure 2: Pulsar and companion mass constraints for PSR J1012$+$5307. Green contours are from the estimated $\dot{P_B}^{\rm GR}$ term and red contours are from inclination angle constraint determined from the kinematic term of $\dot{x}$. Both the companion mass ($m_{\rm c}$) and pulsar-companion mass ratio ($q$) contours are determined from measurements from J1012_binary_mass
• Figure 3: Contours of $\Omega_{\text{asc}}$ and $i$ from $\dot{x}$ measurement for J1012$+$5307
• Figure 4: In green, the curve of $m_{\rm c}$ vs $\sin i$ from detected value of $h_3$ for PSR J2145$-$0750. The dashed lines represent the 1, 2, and 3-$\sigma$ error regions. Red and blue shaded region represent the 1-$\sigma$ range of $m_{c}$ and $\sin i$ measurements respectively from J2145_mass_measurement
• Figure 5: Contours of $\Omega_{\text{asc}}$ and $i$ calculated from $\dot{x}$ measurement of PSR J2145$-$0750. The gold region represent the 1-$\sigma$ error region of $\Omega_{\text{asc}}$ determined by calculation of reflex motion of VLBI data using our $\dot{x}$ measurement as a prior.